1. Field of the Invention
The present invention relates to an Optical Network Unit (ONU) management method and an optical line termination, and particularly to an ONU management method and an optical line termination in a Passive Optical Network (PON) system including an Optical Line Termination (OLT) and an ONU or an Optical Network Termination (ONT).
2. Description of the Related Art
At present, as a realization method of an access network with high speed broad band, the introduction of a PON system has been advanced. The PON system is a network system in which plural user side units (ONU: Optical Network Unit) and one station side unit (OLT: Optical Line Termination) are connected in star configuration by an optical splitter and optical fibers, and communication is performed between the units of the OLT-ONU.
As the PON system, an ATM-PON system in which communication is performed in a PON section based on an Asynchronous Transfer Mode (ATM) communication system is standardized by the ITU-T Recommendation G.983 series (see, for example, the ITU-T Recommendation G.983.1). Besides, a Gigabit-capable Passive Optical Networks (GPON) system is standardized by the ITU-T Recommendation G.984 series.
For example, in the ATM-PON system, as described in the ITU-T Recommendation G.983.1, in order to establish communication between OLT-ONU and to perform ONU connection, a series of processings called the ranging flow is performed. The ranging flow processing is such a function that distances between OLT-ONU are measured, transmission timings of up signals from the ONUs to the OLT are determined for the respective ONUs, and collision of the up signals is prevented. When the distances are measured in the ranging flow processing, in order to prevent the collision of ONU responses at the time of the measurement, it is necessary to cause the ONUs to respond one by one. For that purpose, a unique serial number of the ONU is used. That is, the ONU serial number is designated to specify the ONU which may respond. In the OLT, a number (identifier) for ONU identification, called a PON-ID, is assigned to an ONU whose ONU serial number has been found and whose distance has been also measured, and after that, the ONU is specified by the PON-ID, and a message is exchanged between the OLT-ONU.
Although the ONU identifier is described as “PON-ID” in the after-mentioned ITU-T Recommendation G.983.1, there is a case where it is described as “ONT-ID” or “ONU-ID” according to documents.
The unique serial number of the ONU is defined by information of 64 bits, and it is defined such that the 32 upper bits indicate a vender ID (fixed value for each vender) to represent a vender, and the 32 lower bits indicate a vender definition part which can be arbitrarily defined by the vender. For example, in the vender definition part of 32 bits, “manufacturing date and serial number are assigned”, or “all of the 32 bits are made serial number”, so that the respective ONUs have different serial numbers and the ONUs can be identified.
In the ranging flow processing, the ONU connection is performed using the unique serial number of the ONU. As the ONU connection method, for example, two methods (Method A, Method B) are described in 8.4.1.1 of the ITU-T Recommendation G.983.1. The Method A is a method in which for example, the serial number of the ONU is registered from an operation system (OpS) to the OLT. The Method B is a method in which for example, the serial number of the ONU is not registered from an operation system to the OLT.
In the case of the Method B, although the ONU serial number is not registered to the OLT from the operation system, in order to establish the communication between the OLT-ONU, it is necessary for the OLT side to specify the serial number of the ONU. Thus, a procedure is required in which the OLT side searches for the ONU serial number. The search of the ONU serial number is such that various bit patterns (for example, several lower bits, etc.) are simply tried among 64-bit patterns of the ONU serial number, and the bit pattern consistent with the serial number of the connected ONU is found by the presence/absence of the response from the ONU. The ITU-T Recommendation G.983.1 III.2 describes an example of the search method of the ONU serial number.
Besides, there is known a system in which when a current system of plural ONUs constituting a redundant configuration and a spare system are switched over, a switch at the ONT side is set, so that the same ONU identifier is used after and before the switching (see, for example, JP-A-2005-45566). There is also known a system in which in a redundant configuration, a current system and a spare system have the same subscriber unit information (serial number) (see, for example, JP-A-2003-244179).
When the ranging flow processing is performed and the PON-ID is assigned to the connected ONU, the subsequent message between the OLT-ONU is exchanged by specifying the ONU with the PON-ID. Thus, in the case where setting is performed individually for the ONU, it is expected that the individual setting data is correlated with the PON-ID and is stored. Under such circumstances, for example, in the case where a failure occurs in an ONU, and the ONU is replaced, it is desired that the PON-ID assigned before the replacement is assigned also to an ONU after the replacement, and the individual setting data before the replacement is succeeded and set.
According to the ITU-T Recommendation G. 983.1, the procedure of the ONU replacement is not specified. In case the Method A of the ITU-T Recommendation G. 983.1, that is, the method of previously registering the ONU serial number from the OLT is adopted, since the serial number of the new ONU is known at the OLT side also at the time of the ONU replacement, the ONU serial number of the storage data has only to be rewritten. However, in order to actually perform this method, it is necessary to perform such complicated management that at the time of the ONU replacement, an ONU installation worker and an operation system administrator communicate with each other in real time, and the new ONU serial number is inputted from the operation system to the OLT, or the ONU serial number is previously informed to the operation system administrator, and the ONU with the serial number is certainly distributed to the user as the replacement destination.
In case the Method B of the ITU-T Recommendation G.983.1, that is, the method in which the ONU serial number is not registered from the OLT is adopted, the OLT searches for the ONU serial number by some method and automatically performs the ONU connection. At this time, when the ONU is simply replaced and the new ONU is connected, the PON-ID is newly assigned, and the storage data before the replacement can not be succeeded. Alternatively, it becomes necessary to manually set data again.
Besides, in the method disclosed in JP-A-2005-45566, the setting of the switch and the like are required at the ONU side. In the method disclosed in JP-A-2003-244179, it is necessary that the current system and the spare system have the same serial number.
In view of the above circumstances, the present invention has an object to provide an ONU management method and an optical line termination, in which in a PON system, ONU connection is performed without registering a serial number of an ONU from an operation system to an OLT, and the same PON-ID as that before the ONU is replaced is assigned to a new ONU after the replacement. Besides, another object of the invention is that setting data before replacement is succeeded also after the replacement.
Another object of the invention is to eliminate the necessity that in a PON system, at the time of ONU installation or replacement, an ONU installation worker and an operation system administrator communicate with each other in real time, and an ONU serial number is inputted from an operation system to an OLT. Besides, another object of the invention is to eliminate the necessity that ONU setting data is set again after ONU replacement, and to enable the ONU replacement to be facilitated.